Generation of tumors. A tumor is an abnormal mass of tissue that results from excessive cell division that is uncontrolled and progressive, also called a neoplasm. Tumors perform no useful body function. They may be either benign (not cancerous) or malignant.
Tumorigenesis is the formation of tumors in the body, often caused by oncogenes. These tumors are the result of uncontrollable reproduction (cell division) due to alterations in the cell's genetic code, creating lesions in the tissue where they reside.